The possible forms of comparison would be:
1) Carla <u>es más alta que </u>Cristina. (Carla is taller than Cristina.)
This type of comparison follows the next order:
verb <em>ser</em> + <em>más </em>+ adjective + <em>que.</em>
2) If we want to be precise, we could add the exact information and say:
Carla es<u> 5 centímetros </u>más alta que Cristina.
3) We could also say that 'Cristina is shorter than Carla.'
Cristina es más baja que Carla.
We use the same construction, but we just change the adjective <em>alta</em> (tall) for <em>baja</em> (short).
4) And finally, in Spanish, we can say that 'Cristina is <em>less tall</em> than Carla.'
Cristina es menos alta que Carla.
In this case, we just apply the adverb <em>menos</em> meaning <em>less.</em>